The invention relates to a calculation device for a radar apparatus, a radar apparatus and calculation method and program for the radar apparatus.
Regarding algorithms for estimating an arrival direction of a radar wave received by an array antenna, DBF (Digital Beam Forming), PRISM (Propagator method based on an Improved Spatial-smoothing Matrix), MUSIC (Multiple Signal Classification), ESPRIT (Estimation of Signal Parameters via Rotational Invariance Techniques) and the like have been known (for example, refer to Patent Documents 1 to 3).    Patent Document 1: JP-A-2005-49123    Patent Document 2: JP-A-2003-14843    Patent Document 3: JP-A-2009-74990
In the high-precision algorithms using eigenvalues or eigenvectors of a correlation matrix, such as MUSIC and ESPRIT, it is necessary to preset the number of incoming waves whose angles can be separated (hereinafter, referred to as the number of separable angles or the separable-number), before estimating the arrival direction.
Here, if the received incoming wave is ideal, even though the number of separable angles is larger than the number of incoming waves, when the number of targets actually existing is one (1), as shown in FIG. 1, an angle spectrum exhibits one peak. However, in reality, as shown in FIG. 2, two or more peaks are generated for one target due to multi-paths having correlatively with a desired wave, so that an angle may be separated. Also, the method of setting the number of separable angles larger than the number of incoming waves and thus calculating an angle spectrum increases a calculation load.
Accordingly, it is preferable to set the same number of separable angles as the number of incoming waves by developing the eigenvalues of the correlation matrix by the respective reception signals before estimating the arrival direction. The number of incoming waves is obtained by using the known algorithm of estimating the number of incoming waves, such as AIC (Ahaike Information Criteria) and MDL (Minimum Descritim Length). However, the precision of the process of estimating the number of incoming waves is low and a difference of one or two occurs in many cases. Also, like an on-vehicle radar apparatus, there is a limit in hardware resources such as capability of a useable calculation circuit. Also, since a relative relation between an own-vehicle and the other vehicle is rapidly changed, it is difficult to estimate the appropriate number of incoming waves regarding specifications in which it is necessary to obtain the angle spectrum with a period of several tens of milliseconds.